The difficulty of applying uniform plastic coatings to the interior of pipe and other tubular goods increases in proportion to the diameter and length of the pipe. Epoxy is one of the most satisfactory plastic coatings for oilfield pipe. An epoxy coating preferably is applied in powdered form to the heated, rotating pipe interior, where the plastic is fused into a continuous film and thereafter the pipe is cooled as the film solidifies to provide a superior coating which protects the metal pipe surface from chemically reacting with the material flowing therethrough, thereby elongating the life of the pipe.
In my co-pending patent application Ser. No. 704,965, filed July 13, 1976, now U.S. Pat. No. 4,089,998 issued May 16, 1978, there is taught a novel process by which pipe is coated in the above manner. The present patent application provides improvements over this previous process. As pointed out therein, the inside peripheral wall surface of a heated pipe can be coated in a superior manner by passing a pocket comprised of a dense, fluidized bed of plastic through the interior of a heated, rotating pipe so that the hot interior surface of the pipe is contacted by the plastic particles, whereupon the particles fuse to the inside wall of the pipe, thereby causing a uniform, continuous plastic coating to be achieved which was superior to other coatings known at that time. Following this discovery, Applicant has found other useful and novel processes by which the pocket of dispersed plastic particles can be transferred into and forced through the pipe in order to achieve an unexpected coating advantage. This new discovery is especially beneficial in coating large diameter pipe of considerable length, and this new process is the subject of this patent application.